The vehicular frame member such as the side member, the cross member, the side sill or the pillar of an automobile is constructed as a hollow member by assembling a main part having a channel-shaped section and an auxiliary part for closing the open face of the main part. Here, the “side faces” and the “bottom face” of the main part are named for the case, in which the open face corresponds to the upper face, for conveniences of description. For example, in case the vehicular frame member is directionally changed to face the “bottom face” sideways, the open face opposed to the “bottom face” is also directed sideways so that one of the “side faces” becomes the upper face whereas the other becomes the bottom face.
The main part of the vehicular frame member is demanded to have a high structural strength and rigidity on one hand, and lightweight and inexpensive as an automotive member on the other hand. For the latter demand, a thin metal sheet (or a steel sheet) is ordinarily used for producing the main part. This is because the main part may be deformed in its sectional shape, when it is subjected to an external force such as tension, compression or twist, and may be lowered in the structural strength and rigidity. For this apprehension, a necessary number of bulkheads are mounted for the reinforcement in the necessary portions in the main part thereby to suppress or prevent the reduction in the structural strength and rigidity. This reinforcement makes compatible high strength and lightweight, as demanded for the vehicular frame member.
The bulkhead in the prior arts is constructed, as disclosed in JP-A-2004-306777, for example, such that connecting wings individually projected over the three sides of a partition face having a shape contoured to the sectional shape of the main part are individually folded at the sides, formed as the folded edges, of the partition face. This bulkhead is fixed to the main part by welding the individual connecting wings to the both side faces and the bottom face of the main part while separating the compartments of the main part in the extending direction.
The bulkhead is demanded to have such a high structural strength and rigidity as can reinforce the vehicular frame member. This demand is a problem how to suppress or prevent the buckling, bending or deformation of the partition face or the folded edges. In this case, it can be exemplified to provide a bulkhead having a peripheral wall section formed by jointing vicinities of the folded edges of the three connecting wings and an auxiliary flange plate which is folded at a folded edge formed at such a side of the partition face as lacks the connecting wing. As a result, existence of the peripheral wall section enclosing the partition face enhances the modulus of section of the partition face to prevent from buckling, bending or deformation of the partition face, and thereby to raise the structural strength and rigidity as the bulkhead.
The bulkhead disclosed in JP-A-11-078978 adopts the structure, in which not only the three connecting wings connected to the individual side faces and the bottom face of the main part, as described above, but also one connecting wing projected over the remaining side of the partition face is folded oppositely of those three connecting wings. The connecting wing thus folded backward is welded to the main part with its two ends contacting with the flanges which are formed across the open face of the main part. This bulkhead is enabled, by the connecting wings alternately folded, to raise the modulus of section of the partition face near the open face of the main part, thereby to suppress or prevent buckling, bending or deformation of the partition face and to raise the structural strength and rigidity as the bulkhead.